1. Field of the Invention
The present invention relates to an audio data processing apparatus for fade-in and/or fade-out effects.
2. Description of the Related Art
For music distribution via the Internet, normally audio signal is encoded using compression coding. One typical compression format for audio data is MP3 (ISO/IEC11172-3) of the Motion Picture Expert Group Phase 1 (MPEG1). Another typical format is ISO/IEC 13818 and ISO/IEC14496, also known as AAC (Advanced Audio Coding) of the Motion Picture Expert Group phase 2 (MPEG2) standard, which can encodes audio signal with 20% to 50% less data than MP3, although AAC is not compatible with MP3. Since AAC makes it possible to express the high quality audio signal with a small amount of data, it has been widely used for music distribution.
Nowadays the playback of music is done at variety of situations. For example, it is replayed as ring tone of cellular phone and/or as alarm sound of scheduler function implemented in PDA or cellular phone. In this situation, fade-in and/or fade-out effects are desirable to make ring tone and/or alarm sound comfortable, and to avoid sudden loud sound.
Japanese patent publication No. 7-220394A discloses a method of processing encoded audio data for fade-in and fade-out effects. According to the method, fade-in is achieved by the step of, decoding the first n samples of data, increasing the amplitude of decoded PAM (Pulse Amplitude Modulation) samples gradually, and encoding the PAM samples again. According to the method, fade-out is achieved by the step of, decoding the last n samples of data, decreasing the amplitude of decoded PAM samples gradually, and encoding PAM samples again.
However, according to the above-mentioned method, it requires high computing speed and large memory size for decoding audio data, changing the amplitude of PAM samples to change the volume of audio signal as time advances, and encoding the PAM samples again. Since the computing speed and memory size of cellular phone are limited, it is difficult to perform above-mentioned method on a cellular phone.